We all know there will be a phone version (definitely ARM and maybe Intel too), and a tablet version (definitely Intel). So it shouldn't be much extra effort to built and support a ARM tablet version. No desktop mode, only Metro/Modern.
Then again, I'd love to see a Surface 3 with Intel Atom or Core M.

The future of Windows support on ARM is unknown at this point, except as Cthungha said, the phone will obviously run ARM. It's possible that Windows for tablet and Windows on phone will converge, but whether they will be the same OS, like iOS on iPhone and iPad, I don't believe that is clear yet.